In recent years, regulations aimed at hazardous substances such as NMOG (Non-methane Organic Gas) and NOx etc. remaining in the exhaust gas of internal combustion engines for automobiles (hereinafter referred to as “engine”) have been becoming stricter to decrease the burden on the environment. For example, PZEV (Partial Zero Emission Vehicle), established by the state of California in the United States of America, is one of the most severe regulations, and few automobiles among the currently marketed automobiles satisfy the regulation. As a result, an exhaust gas purifying device for engines has been demanded that has higher exhaust gas purification ability.
Generally, an exhaust gas purifying device is provided with a catalytic converter in an exhaust gas flow path, and purifies NMOG, NOx, etc. with this catalytic converter. With an exemplary exhaust gas purifying device, the catalytic converter is provided directly below the engine so that high temperature exhaust gas is supplied thereto and the time taken to warm up can be shortened.
However, since catalyst degradation due to heat is intense with such a device, it is necessary to increase the amount of noble metal used in order to supplement the performance decline due to thermal degradation, which leads to high cost.
Consequently, in the exhaust gas purifying device illustrated in Patent Document 1, a first catalytic converter is provided directly below the engine, and a second catalytic converter that is separated from this first catalytic converter is provided under the floor of the automobile (refer to Patent Document 1). According to this device, the performance decline due to heat degradation can be suppressed since exhaust gas in a somewhat lowered temperature state is supplied to the second catalytic converter.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-278100